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This density functional theory (DFT) study explores the efficacy of cooperative catalytic systems in enabling the ionic hydrogenation of N2 with H2, leading to NH3 formation. A set of N-heterocyclic carbene-based pincer tungsten/molybdenum metal complexes of the form [(PCP)M1(H)2] (M1 = W/Mo) were chosen to bind N2 at the respective metal centres. Simultaneously, cationic rhodium/iridium complexes of type [Cp*M2{2-(2-pyridyl)phenyl}(CH3CN)]+ (Cp* = C5(CH3)5 and M2 = Rh/Ir), are employed as cooperative coordination partners for heterolytic H2 splitting. The stepwise transfer of protons and hydrides to the bound N2 and intermediate NxHy units results in the formation of NH3. Interestingly, the calculated results reveal an encouraging low range of energy spans ranging from ∼30 to 42 kcal mol−1 depending on different combinations of ligands and metal complexes. The optimal combination of pincer ligand and metal center allowed for an energy span of unprecedented 29.7 kcal mol−1 demonstrating significant potential for molecular catalysts for the N2/H2 reaction system. While exploring obvious potential off-cycle reactions leading to catalyst deactivation, the computed results indicate that no increase in energy span would need to be expected. [ABSTRACT FROM AUTHOR]

CO and H 2 S poisoning of Pt-based catalysts for hydrogen oxidation reaction (HOR) stands as one of the long-standing hindrances to the widespread commercialization of proton exchange membrane fuel cells. In this paper, a Ru/Ti 4 O 7 catalyst is successfully synthesized by the microwave-thermal method. This Ru/Ti 4 O 7 catalyst shows a much higher noble metal mass activity than those of commercial PtRu/C and conventional Ru/C catalysts. The performance of the Ru/Ti 4 O 7 catalyst under the exist of CO or H 2 S shows insignificant current decay, which is far superior to commercial PtRu/C and Pt/C catalysts. In this Ru/Ti 4 O 7 catalyst, the electron transfer between Ru and Ti to form d-p orbital hybridization is considered to be responsible for the favorable catalytic HOR performance and the corresponding CO and H 2 S tolerance. The interaction mechanism formed by electron transfer may open a promising way for the subsequent development of anti-poisoning catalysts for PEM fuel cell hydrogen oxidation reaction. [Display omitted] • Ru/Ti 4 O 7 catalyst shows a superior noble metal mass activity than those of commercial Pt–Ru/C based catalysts. • Ru/Ti 4 O 7 catalyst exhibits excellent resistance to CO poisoning. • The catalyst is extremely resistant to H 2 S while remaining CO-tolerant. • MSI of Ru/Ti 4 O 7 ensures catalytic activity and anti-poisoning properties. [ABSTRACT FROM AUTHOR]

To replace the noble metals used in hydrodeoxygenation (HDO) catalysts, guaiacol HDO was conducted using various transition metal-loaded catalysts. Co/TiO2 was highly active for guaiacol HDO, enabling a more economic removal of the methoxy groups compared to the Ru/TiO2 catalyst, resulting in superior cyclohexanol selectivity. When a WO3 promoter was added to the Co catalyst to enhance its oxygen removal ability, the conversion of guaiacol was severely reduced because the co-impregnated WOx species decreased the number of exposed Co sites. To avoid this phenomenon, Co and WO3 were isolated by physically mixing Co/TiO2 and WO3/TiO2, where 100% conversion and oxygen removal could be achieved under 10 bar H2 at 250 °C. The cause of the catalyst deactivation was systematically investigated by magnetic separation of the physical mixture of the catalysts after the reaction, followed by a series of characterization studies. Temperature-programmed-oxidation mass spectroscopy and Raman spectroscopy revealed that the deposition of carbonaceous species was the main contributor to the deactivation of WO3/TiO2, and the catalytic activity could be successfully recovered by simple calcination at 400 °C. This study provides insights into the development of economical and efficient physically mixed HDO catalysts using transition metals, and contributes to the understanding of the deactivation and regeneration of physically mixed HDO catalysts. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolysis (PEMWE) can be coupled with renewable energy power generation technology and is considered to be a highly promising hydrogen production technology. However, the acidic electrolyte environment, as well as the numerous sulfonic acid groups on the proton exchange membrane surface, can seriously corrode the oxygen evolution reaction (OER) catalyst and even cause deactivation. To develop an efficient acidic OER catalyst, the IrOx/WO3 heterostructure OER catalyst was prepared by a hydrothermal-calcination method. The coordination environment of IrOx was regulated through the electronic rearrangement effect, improving the OER activity and stability of the catalyst in acidic media. The prepared IrOx/WO3 exhibits excellent OER activity in 0.5 M H2SO4, with an overpotential of only 260 mV to achieve a current density of 10 mA cm−2 and a mass activity of 176.8 A gIr−1. It can stably operate for over 12 hours at a current density of j = 10 mA cm−2. [ABSTRACT FROM AUTHOR]

[Display omitted] • SO 2 poisons the SCR catalysts and lead to the catalyst deactivation. • This paper reviews sulfur poisoning mechanism of SCR catalysts and anti-sulfur measures. • Formation of sulfates block catalyst pore and cover active sites, causing sulfur poisoning. • Doping element and modifying morphology protect active sites and alleviate sulfate deposition. • Thermal regeneration and water-washing regeneration are most common regeneration methods. Selective catalytic reduction (i.e., SCR) denitrification has become the most popularly used denitrification technique owing to its high denitrification efficiency, clean process, and mature reliability. However, SO 2 in the flue gas stream can poison catalysts and lead to catalyst deactivation. Thus, it is of great significance to investigate the poisoning mechanisms and anti-sulfur poisoning measures of the catalysts. This paper systematically reviews the sulfur poisoning mechanisms of several SCR catalysts (e.g., vanadium-based, cerium-based, manganese-based, copper-based, and iron-based), anti-sulfur measures (including doping of metal and non-metal elements, the use of carriers, and the control of catalyst morphology and structure). Results showed that the sulfur poisoning mechanisms of SCR catalyst mainly includes formation of ammonium sulfates and metal sulfates to block the catalyst pore and cover the active sites, competitive adsorption of SO 2 and NO x , and the consumption of active components caused by SO 2. Doping other elements and modifying morphology and structure of catalyst can protect the active sites of catalysts and alleviate the sulfate deposition and pore blockage issues. Doping elements can raise the denitrification efficiency of the catalyst by more than 20–70%, and modifying morphology and structure of catalyst can increase the denitrification efficiency by about 20%. Besides, regeneration of sulfur-poisoning catalyst was also reviewed. The most common methods of sulfur-poisoning catalysts regeneration are thermal regeneration and water-washing regeneration. Finally, some suggestions and prospects for design and development of anti-sulfur poisoning SCR catalyst in the future are commented. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mn/TiO 2 {0 0 1} exhibited better low-temperature NO conversion and K resistance. • K did not decrease the specific surface area of Mn/TiO 2 {0 0 1}. • K had a greater effect on NO adsorption and activation and was more likely to affect the L-H mechanism. The presence of alkali metals in the flue gas can physically and chemically poison the catalyst, leading to catalyst deactivation. In this paper, Mn/TiO 2 catalysts with exposed TiO 2 {0 0 1} (NS) and TiO 2 {1 0 1} (NP) facets are studied for potassium poisoning. It was found that Mn/TiO 2 -NS exhibited higher denitrification efficiency and tolerance to potassium compared to Mn/TiO 2 -NP. Experimental characterizations and DFT calculations showed that the NH 3 -SCR reaction on the surface of both fresh Mn/TiO 2 -NS and Mn/TiO 2 -NP catalysts was controlled by the E-R and L-H mechanisms. The presence of K species did not decrease the specific surface area of Mn/TiO 2 -NS catalyst. Under the same K poisoning condition, Mn/TiO 2 -NS was able to retain more surface acidic sites and surface active species, whose reaction was still controlled by the E-R and L-H mechanisms. While the adsorption and activation of NO on the Mn/TiO 2 -NP surface was severely inhibited by the presence of K, resulting in the L-H mechanism blocked. [ABSTRACT FROM AUTHOR]

Ni-based catalysts have been widely used for the CO2 reforming of methane (CRM) process, but deactivation is their main problem. This study created an alternative electronic Ni-NiO-CeO2 interaction on the surface of 5 wt% Ni-5 wt% CeO2/Al2O3-MgO (5Ni5Ce(xh)/MA) catalysts to enhance catalytic potential simultaneously with coke resistance for the CRM process. The Ni-NiO-CeO2 network was developed on Al2O3-MgO through layered double hydroxide synthesis via our ammonia vapor diffusion impregnation method. The physical properties of the fresh catalysts were analyzed employing FESEM, N2 physisorption, and XRD. The chemical properties on the catalyst surface were analyzed employing H2-TPR, XPS, H2-TPD, CO2-TPD, and O2-TPD. The CRM performances of reduced catalysts were evaluated at 600 °C under ambient pressure. Carbon deposits on spent catalysts were determined quantitatively and qualitatively by TPO, FESEM, and XRD. Compared to 5 wt% Ni-5 wt% CeO2/Al2O3-MgO prepared by the traditional impregnation method, the electronic interaction of the Ni-NiO-CeO2 network with the Al2O3-MgO support was constructed along the time of ammonia diffusion treatment. The electronic interaction in the Ni-NiO-CeO2 nanostructure of the treated catalyst develops surface hydroxyl sites with an efficient pathway of OH* and O* transfer that improves catalytic activities and coke oxidation. [ABSTRACT FROM AUTHOR]

Employing catalytic decomposition to break down reducing agents in intermediate-level radioactive waste during nuclear fuel reprocessing offers significant advantages. This study focuses on investigating the deactivation behavior of 5% Ru/C catalysts by two different synthesis processes used for reducing agent destruction. Deactivation experiments were conducted by subjecting the 5% Ru/C catalysts to 100 and 150 reaction cycles. Changes in the concentration of free radicals on the carbon-based carrier were measured to analyze the loading position and loss of Ru ions. Additionally, sorption–desorption curves and pore size distributions of the four catalysts were obtained. Analysis results reveal that Ru ions on the catalyst adsorb onto active free radical sites on the carbon-based carrier. Under ultrasonic conditions, some Ru ions partially desorb from the free radical sites on the carbon-based carrier, and desorbed Ru ions may adsorb onto weak free radical sites, while undesorbed Ru ions may adsorb onto strong free radical sites. After hundreds of hours of reaction, SM1 and SM2 exhibited approximately a 30% decrease in specific surface area and pore volume compared to SM0. However, the catalyst activity remained unchanged, and the catalyst pore size remained essentially unchanged, which primarily means that the micropores on the catalyst's surface have undergone corrosion and damage. [ABSTRACT FROM AUTHOR]

Manganese oxide-cerium oxide supported on titanate nanotubes (i.e., MnCe/TiNTs) were prepared and their catalytic activities towards NH3-SCR of NO were tested. The results indicated that the MnCe/TiNT catalyst can achieve a high NO removal efficiency above 95% within the temperature range of 150–350 °C. Even after exposure to a HCl-containing atmosphere for 2 h, the NO removal efficiency of the MnCe/TiNT catalyst maintains at approximately 90% at 150 °C. This is attributed to the large specific surface area as well as the unique hollow tubular structure of TiNTs that exposes more Ce atoms, which preferentially react with HCl and thus protect the active Mn atoms. Moreover, the abundant OH groups on TiNTs serve as Brønsted acid sites and provide H protons to expel Cl atom from the catalyst surface. The irreversible deactivation caused by HCl can be alleviated by H2O. That is because the dissociated adsorption of H2O on TiNTs forms additional OH groups and relieves HCl poisoning. [ABSTRACT FROM AUTHOR]

The commercialization of a polymer membrane H2–O2 fuel cell and its widespread use call for the development of cost‐effective oxygen reduction reaction (ORR) nonplatinum group metal (NPGM) catalysts. Nevertheless, to meet the requests for the real‐world fuel cell application and replacing platinum catalysts, it still needs to address some challenges for NPGM catalysts regarding the sluggish ORR kinetics in the cathode and their poor durability in acidic environment. In response to these issues, numerous efforts have been made to study NPGM catalysts both theoretically and experimentally, developed these into the atomically dispersed coordinated metal–nitrogen–carbon (M–N–C) form over the past decades. In this review, we present a comprehensive summary of recent advancements on NPGM catalysts with high activity and durability. Catalyst design strategies in terms of optimizing active‐site density and enhancing catalyst stability against demetalization and carbon corrosion are highlighted. It is also emphasized the importance of understanding the mechanisms and principles behind those strategies through a combination of theoretical modeling and experimental work. Especially, further understanding the mechanisms related to the active‐site structure and the formation process of the single‐atom active site under pyrolysis conditions is critical for active‐site engineering. Optimizing the active‐site distance is the basic principle for improving catalyst activity through increasing the catalyst active‐site density. Theoretical studies for the catalyst deactivation mechanism and modeling stable active‐site structures provide both mechanisms and principles to improve the NPGM catalyst durability. Finally, currently remained challenges and perspectives in the future on designing high‐performance atomically dispersed NPGM catalysts toward fuel cell application are discussed. [ABSTRACT FROM AUTHOR]

This study consists of four main parts. First, a heterogeneous reactor model was developed to simulate a diesel hydrodesulfurization (HDS) reactor with catalyst deactivation. Second, operating conditions were investigated. Third, the simulation results from the first part were modeled using the response surface method and artificial neural networks (ANNs) to shorten the temperature path optimization time. Among the different modeling methods, the feed-forward ANN method employing the Bayesian Regularization (BR) training method with 10 neurons in the hidden layer demonstrated the highest accuracy. Finally, the temperature path of the trickle bed reactor was optimized. A three-dimensional curve depicting sulfur output content versus temperature and catalyst operation time was plotted using the most effective ANN approach as a fitness function. When the sulfur content met the Euro-6 requirement, the temperature path versus catalyst working period was optimized. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of flower-like hollow Ni 0.5 /xMgO-Al 2 O 3 catalysts were synthesized. • Ni 0.5 /xMgO-Al 2 O 3 catalysts have high specific surface area and thermostability. • Moderate Mg addition can promote the generation of spinels and then Ni x Mg y O. • More generation of spinels and Ni x Mg y O leads to stronger MSI and alkalinity. • Ni 0.5 /0.5MgO-Al 2 O 3 shows excellent DRM activity and high coking resistance. Dry reforming of methane (DRM) suffers catalysts deactivation due to severe coking. Ni/MgO-Al 2 O 3 is a promising system for DRM catalysts with high coking resistance, as the addition of MgO in Ni/Al 2 O 3 catalysts can improve the alkalinity of the support and enhance the metal-support interaction. However, so far the activity and stability of Ni/MgO-Al 2 O 3 is still unsatisfactory while the role of Mg addition remains unclear. In this paper, a series Ni 0.5 /xMgO-Al 2 O 3 catalysts with flower-like hollow sphere morphology and high surface area were synthesized via a facile hydrothermal method. Appropriate Mg addition promotes the formation of NiAl 2 O 4 while more Mg addition leads to the formation of Ni x Mg y O. Both cases can enhance the MSI of the catalysts without changing the morphology of the catalyst. More Mg addition also leads to stronger CO 2 adsorption via improving the alkalinity. Nevertheless, overdose of Mg results in weaker MSI and the blockage of Ni active sites. Ni 0.5 /0.5MgO-Al 2 O 3 with moderate Mg addition shows excellent activity (CH 4 ∼ 75 %, CO 2 ∼ 85 %) and stability (>100 h) at a high GHSV = 144000 ml/g cat ·h−1 and 800 °C with nearly no coking formation (<0.8 wt%). This work helps reveal the role of MgO addition in Ni/Al 2 O 3 systems and gives new insights into the design of DRM catalysts with high activity and stability. [ABSTRACT FROM AUTHOR]

• Ca-based catalysts are promising in both conventional DRM and CaLDRM processes. • Roles and mechanisms of Ca in various DRM catalyst formulas are summarized. • CaO enhances the metal-support interaction and promotes the dispersion of metals. • The increased basicity by CaO accelerates the CO 2 adsorption and coke gasification. • The presence of Ca in mineral catalysts promotes the creation of lattice defects. Dry reforming of methane (DRM) is a promising and well-studied process that could simultaneously convert the two most abundant greenhouse gases (CH 4 and CO 2) to syngas (CO and H 2). The main obstacle for this reaction, however, is the easy catalyst deactivation caused by coke deposition. Various catalysts have been developed and employed, among which calcium (Ca)-based catalyst is one of the most economically feasible options for industrial scaling-up due to its low cost, easy availability, non-corrosiveness and environmental friendliness. In this paper, therefore, a comprehensive summary of the role and mechanism of Ca-based catalysts in DRM reaction was presented. Specifically, the deactivation behaviors and mechanism of conventional catalysts in DRM reaction were introduced. Subsequently, the role of Ca in various catalyst formulas as a support, a promoter, or a constituent element in specific mineral phases such as perovskites were summarized, and meanwhile the effect of different preparation methods on the performance of Ca-based catalysts was described. As the most widely used agent for CO 2 capture, the employment of Ca-based materials in chemical looping dry reforming of methane was also reviewed. Furthermore, the integration of Ca-based catalysts in some novel catalysis systems such as the membrane catalysis and plasma catalysis systems were briefly surveyed. Finally, the future prospects were proposed, in order to provide a guidance for the development and application of Ca-based catalysts in DRM reaction. [ABSTRACT FROM AUTHOR]

Deactivation of catalyst for the oxidation of carbon monoxide in the impurity gases such as CO2, SO2, and NOx are common issues in practical use. In this work, Cu–Mn–Ce composite oxide catalysts (CMCO) were coupled with K2CO3 (KC) to inhibit the poisoning effect of these gases. The CMCO/KC composite catalysts, prepared by multi-step impregnation method, were tested for CO catalytic oxidation and CO2 chemical absorption in the presence of SO2 (0.004% and 0.04%) or NO2 (0.0025% and 0.025%), and further characterized by XRD and XPS. The results showed that CMCO/KC could catalyze CO efficiently at low temperatures, and proper K2CO3 addition (10–50 wt%) could even promote CMCO catalytic activity owing to the CO2 sorption. Among them, CMCO/50KC showed the highest CO catalytic performance with the T50 of 114.5 °C. More importantly, K2CO3 doping treatment could reduce or eliminate the catalyst deactivation caused by SO2 and NO2, due to the competitive sorption reaction of the alkali toward the acid gases. Further regeneration experiments revealed that CMCO/KC also had fine regeneration activity and stability for CO/CO2 removal. [ABSTRACT FROM AUTHOR]

The dry reforming of methane (DRM) is a promising method for controlling greenhouse gas emissions by converting CO2 and CH4 into syngas, a mixture of CO and H2. Ni-based catalysts have been intensively investigated for their use in the DRM. However, they are limited by the formation of carbonaceous materials on their surfaces. In this review, we explore carbon-induced catalyst deactivation mechanisms and summarize the recent research progress in controlling and mitigating carbon deposition by developing coke-resistant Ni-based catalysts. This review emphasizes the significance of support, alloy, and catalyst structural strategies, and the importance of comprehending the interactions between catalyst components to achieve improved catalytic performance and stability. [ABSTRACT FROM AUTHOR]